Final answer:
Memory B cells bear BCRs with somatically hypermutated, isotype switched immunoglobulin genes. Their antigen-binding diversity is created by V, D and J segment rearrangement, and specificity is retained after class switching to different antibody types like IgM, IgG, IgA, or IgE.
Step-by-step explanation:
Memory B cells are crucial components of the adaptive immune system. After encountering an antigen, these cells undergo a variety of genetic modifications to enhance their future response to that specific antigen. Firstly, genetic rearrangement leads to diversity in the variable regions of B cell receptors (BCRs), utilizing V (Variable), D (Diversity), and J (Joining) segments in the heavy chain and V and J segments in the light chain. This genetic diversity allows for the creation of millions of different antigen-binding sites, equipping the B cells to recognize a myriad of antigens.
Upon activation, memory B cells can undergo class switching or isotype switching, a process dictated by cytokines from helper T cells. During class switching, the constant region of the immunoglobulin gene is modified, which alters the class (IgM, IgG, IgA, IgE) of antibodies a plasma cell produces while preserving the epitope specificity determined by the variable region. Thus, the memory B cells have BCRs composed of the somatically hypermutated, isotype switched immunoglobulin genes.
Memory B cells have BCRs that consist of somatically hypermutated, isotype switched immunoglobulin genes. These genes have generated diverse antigen-binding sites through rearrangement and maintained specificity post class-switching.